This invention relates to a system and method for mixture preparation control in an internal combustion engine and more particularly, to a system and method which controls the preheating of the fuel and air mixture within an internal combustion engine prior to entry into the engine""s combustion chamber by the use of electromechanical or electrohydraulic valve actuators for enhanced efficiency and lower exhaust emissions.
Valve timing systems, arrangements and assemblies are used in internal combustion engines in order to alter the timing of the opening and closing of the engine""s intake and/or exhaust valves. Prior valve timing systems typically include one or more camshafts and cam timing assemblies which selectively advance and/or delay the rotation of one or more camshafts relative to the crankshaft, thereby controlling the actuation of the intake and exhaust valves.
These prior systems and valve timing profiles used by these systems suffer from several drawbacks.
Particularly, these prior cam-driven systems are ineffective to dynamically adjust or control valve overlap (i.e., situations in which both the intake and exhaust valves are open), due to their inherent physical limitations. In order to generate maximum power at high speeds, a relatively high degree of valve overlap is required. However, at low speeds (e.g., at idling conditions), a high degree of valve overlap undesirably causes high emissions and poor fuel efficiency. Additionally, low fuel/air mixture velocities in the intake ports at low engine speeds compound the problems. During cold starts and idling prior to engine xe2x80x9cwarm upxe2x80x9d, liquid fuel usually forms a pool in the intake port and possibly enters the combustion chamber as a stream during intake valve opening. This results in undesirable oil degradation, fuel waste, and higher hydrocarbon emissions.
Due to the inability of these prior systems to efficiently and dynamically adjust the timing of the valves during different vehicle operating modes, the valve timing profiles used within these prior systems are typically a compromise between power output at high engine speeds and proper idling at low engine speeds. The compromise is generally designed to favor the production of output power, good efficiency, and lower exhaust emissions at higher engine speeds. However, relatively high exhaust emssions, low fuel economy and poor efficiency of the engine at idle speeds remain as undesirable drawbacks.
Efforts have been made to increase the efficiency of vehicle engines and reduce emissions by eliminating the camshafts and operating the intake and exhaust valves through the use of selectively controllable electromechanical or electrohydraulic actuators. These types of systems eliminate many problems related to the physical characteristics of cam-driven systems and offer additional flexibility in valve timing. However, these prior camless systems are typically implemented using conventional cam-driven valve timing, and thus, suffer from many of the same previously delineated drawbacks. For example and without limitation, the valve timing used within these systems is typically calibrated or programmed during the manufacturing process and is not dynamically controllable during the operation of the vehicle. As a result, the valve""s timing again typically compromises between power output at high engine speeds and proper idling at low engine speeds in a manner similar to the prior cam-driven systems. Hence, these systems still fail to provide fuel efficiency and low exhaust emissions at idle speeds. Additionally, because these timings are typically xe2x80x9csetxe2x80x9d or xe2x80x9cfixedxe2x80x9d during manufacture, they are unable to be selectively and dynamically altered to control the engine to achieve maximum efficiency during both high engine speeds and idle operation of the vehicle. In addition, the fuel/air mixture is still susceptible to fuel condensation, liquid streaming into the combustion chamber, and low charge flow velocities at idle.
There is therefore a need for a new and improved valve actuation system for use with a camless engine which overcomes the drawbacks associated with low speed operation of an internal combustion engine. The Applicants"" invention addresses these drawbacks and provides a system and a method for dynamically controlling the valve timing events of the camless engine and which compensates for the effects of low speed idle on engine efficiency, fuel economy and exhaust emissions.
It is a first object of the invention to provide a system and method for the control and preparation of the combined fuel and air mixture in an internal combustion engine, which overcomes at least some of the previously delineated drawbacks of the prior systems, devices, and/or methods.
It is a second object of the invention to provide a method strategy, or methodology, for controlling valve actuators to preheat the combined fuel and air mixture prior to the mixture""s entry into the combustion chamber.
It is a third object of the invention to provide a method for pulsing an intake valve at specific times within a four-stroke engine cycle and during specific engine operating conditions of the internal combustion engine to operate the engine more efficiently and create lower exhaust emissions.
According to a first aspect of the present invention, a valve timing system is provided for use with an internal combustion engine of the type including at least one cylinder having a piston pivotally coupled to a crankshaft and at least one valve which is operatively disposed within a port containing an amount of fuel. The system includes at least one actuator effective to selectively actuate the at least one valve; a first engine sensor effective to measure a temperature of the engine and to generate a first signal representing the temperature; a second engine sensor effective to monitor the angular position of the crankshaft and to generate a second signal representing the angular position; and a controller communicatively coupled to the at least one actuator and the first and second engine sensors, the controller being effective to receive the first and second signals and to cause the at least one actuator to selectively pulse open the at least one valve based upon the received first and second signals.
According to a second aspect of the present invention, a method is provided for controlling valve actuation within a camless internal combustion engine of the type including at least one cylinder having a piston which is pivotally coupled to a crankshaft, at least one intake valve operatively placed in an intake port containing an amount of fuel, and at least one exhaust valve operatively placed in an exhaust port. The method includes the steps of: monitoring positions of the at least one intake valve and the at least one exhaust valve; monitoring a temperature of the engine; monitoring an angular position of the crankshaft; determining if the engine is above or below a predetermined operating temperature; and if the engine is determined to be below the predetermined operating temperature, pulsing open the at least one intake valve when the piston is in an exhaust stroke, effective to introduce a small amount of burnt gas into the intake port, thereby heating the intake port and vaporizing the amount of fuel.
Further objects, features, and advantages of the invention will become apparent from the following detailed description of the preferred embodiment of the invention and by reference to the following drawings.